SOAP UI uses three levels to structure functional tests:
TestSuite: It is a pool of test cases used for combining functional tests into logical units
TestCase: It is a group of test steps that are bring together to test some specific aspect of your services. You can augment any number of testcases to test suites
TestSteps: They are “building blocks” of functional tests in SOAPUI. They together makes TestCase and determines the flow of execution of the service to be tested.